Radio signaling system



Nov. 29, 1927.

J. F. FARRINGTON RADIO SIGNALING SYSTEM Filed April 22.- :935

vJob/7 [Far/709mm- I Patented Nov. 29, 1927.

UNITED STATES PATENT OFFICE.

JOHN F. FARRINGTON, OF FLUSHING, NEW YORK, ASSIGNOR, BY MESNE ASSIGN- MENIS, TO WESTERN NEW YORK.

ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF RADIO SIGNALING SYSTEM.

Application filed April 22, 1925.

This invention relates to signaling systems and more particularly to an oscillation genorator adapted to operate at substantially constant frequency.

An object of this invention is to prevent changes in load impedance from reacting upon the frequency determining circuit of an oscillation generator.

Another object is to provide an oscillation generator capable of producing oscillations of substantially constant frequency.

A feature of the invent? on is the use of the frequency determining circuit of an oscillator tube as the coupling circuit for an amplifier.

These objects and others which will be apparent as the nature of the invention is disclosed, are accomplished in a circuit including an oscillating vacuum tube and an amplifier by employing a balancing condenser forming one branch of a WVheatstone bridge, the other branches of which include the internal capacity of the amplifying tube and the impedances of the frequency determining circuit of the oscillator.

Although the novel features which are believed to be cl'iaractcristic of this invent-ion will be pointed out more particularly in the claims appended hereto, the invention itself, its object and advantages, the manner of its organization and themethod of its operation will be better understood by referring to the following specification taken in connection with the accompanying drawing forming a part thereof in which Fig. 1 is a diagrammatic representation of a radio signaling system embodying this invention; and Fig. 2 shows a modification of the portion of Fig. 1 at the left of the line 2-2.

in Fig. 1 is shown an oscillation generator 1. therein represented as a three-electrode space discharge device although any other suitable means for producing high frequency oscillations may be employed, the frequency of which is determined by an oscillatory circuit comprising inductanccs 3 and 4- connected in the plate and grid circuits respectively and condenser 2 connected across the two inductanccs. Inductances 3 and i are preferably magnetically coupled together although it is not essential to the operation of this invention that therebe coupling between these elements. Space current for the tube is supplied by source 5. Condenser 6 Serial No. 24,916.

is used to form ashunt to source 5 for high frequency oscillations.

The oscillations produced in the above described system are impressed upon the grid filament circuit of space discharge amplifier 7 by means of inductance 4. The output circuit of the amplifier is connected to a variable impedance load L which may be an antenna circuit, a bank of amplifiers or any other suitable circuit the impedance of which may be subject to variations. Space current is supplied to tube 7 by source 8. Balancing condenser 9, the operation of which will be hereinafter set forth, is connected between the anode of the tube 7 and terminal 12 of inductance 3. Capacity 10 represents the grid plate capacity of tube 7 and such additional capacity as is inherent in the socket and connections associated therewith. The capacity 10 may be increased by the addition of a fixed condenser if desired.

In the modification shown in Fig. 2 the capacitative and inductive branches of the oscillating circuit are interchanged. Condensers 13 and 14.- and inductance 15 constitute the frequency determining elements. The value of the inductance or the capacity of the condensers may be varied to alter the frequency. Plate potential is supplied from source 5 through radio frequency choke coil 16. Grid biasing potential is obtained for tube 1 by grid leak resistance 17 and condenser 18, and for tube 7 by battery 19. Choke coils 20 and 21 prevent radio frequency electro-motive forces from. being applied to the sources 17 and 19 respectively which would tend to short-circuit condenser 14. o

Although the above two types of oscillation generators have been specifically described any other suitable type of circuit may be employed and the balance hereinafter de scribed used therewith if desired.

Variations in impedance of load L will change theinput impedance of amplifier 7 due tothe internal grid-plate capacity of tube 7 which couples the -load circuit to the input circuit. Amplifier 7 being connected in parallel with inductance 4: of the oscillating circuit of tube 1 will vary the impedance of that circuit whenever the input impedance of the amplifier tube is changed. Inasmuch as the frequency of the oscillations produced Lil by source 1 determined by the electrical constants of the oscillating circuit, any variation in impedance of the elements of this circuitwill, produce a change of frequency of the oscillations generated by source 1.

Such variation in tl'rcquency is prevented f in taking place however, by condenser 9 \vhicl is connected as described above between the anode of tube 7 and a point in the oscillating circuit the high frequency potential of which is opposite to that of the point to which the grid of tube 7 is connected. The capacity 9, internal capacity 10 of the amplifier tube and inductanccs 3 and l: may be considered to comprise a ll heatstone bridge. Load L connected across two opposite corners of this Wheatstone bridge while the condenser 2 in, the frequency determining circuit of the oscillator, is connected across the other two opposite corners. Under these conditions when the capacity of condenser 9 is adjusted tohave the same ratio to. the internal capacity of tube 7 as the inductance of coil. 4: bears to the inductance of coil 8, at a given frequency, the bridge will be in astate of equilibrium at that frequency with respect to tube 7 as a generator. In this condition currents flowing in branches 3 and 4: from tube 7 as a source will be equal and opposite in direction whereby the effect of these currents on the oscillation circuit as. a whole. will. be neutralized. The same explanation may be referred to Fig. 2 by substitutingcondensers 13: and ll for induct-ances 3 and 4E and inductance 15 for condenser 2. V

It has heretofore, in many cases, been unsatisfactory in oscillation generation systems to employ a single tuned circuit to estab fsh the frequency of oscillations generated and to couple the oscillation generator to an am plifier tube, due to the variation in the frequency of the oscillations as the impedance of the load is varied. By employing the means herein described such variation is substantially prevented.

This invention is particularly useful. in transmitting apparatus where it is desirable to have substantially constant frequency during variation of the impedance of the ldad to which the oscillations are applied. Maintenance of constant 'equency is essential in cases where transmitting channels are relatively close together in frequency, and slight variations in carrier frequency would be suflicient to cause interference with other carrier waves and produce objectionable beats in the receiver. An incidental advantage of this arrangement is that singing of theampliiier circuit due to the internal grid.- plate capacity 10 of amplifier tube 7 is pre vented.

Anyother; well known method of neutralizing the coupling effect of the plate-grid caacey-. 01

paciiy of the amplifier tube may be employed in place of the method herein described if desired.

Although this system has been shown and described as applied. to particular circuits and uses, it is not to be limited thereto but only in accordance with the invention as defined in the. following claims.

lVhat is cla med is:

1. An electrical systen'i comprising two three-electrode space discharge devices and a tuned circuit having a two-part inductance, one device having its electrodes connected to different potential points on said tuned circuit and cooperating therewith to constitute an oscillator, connections whereby oscillations aresupplied from said tuned circuit to the second device, and a connection from one of the electrodes of the second devi e through a condenser to one terminal of,

one part of said inductance to effect neutrali- 'ation of the inter-electrode capacity of said second device.

In an electrical system, an oscillator comprising a space discharge device having input and out-put circuits coupled by a he quency determining circuit including an inductance comprising a plurality of sections, a three-electrode space discharge amplifier associated with a variable load, means for connecting electrodes of said amplifier to one inductancev section, and means for connecting the other electrode of said amplifier through a capacity to said other inductance section.

3. In an electrical system, an oscillator comprising a space discharge device having input and output circuits coupled by a frequency determining circuit including an in ductance comprising a plurality of sect-ions, a tln'ee-electrode space discharge amplifier associated with a variable load, means for directly connecting certain electrodes of said a n 'ililierto one inductance section, and means including a condenser for connecting another electrode of said amplifier to said other inductance section.

l. in a system, an oscillation generator comprising a. three-element space discharge device, a frequency determiningcircuit operati rely associated therewith, a, thrce-olectrode s1 ace discharge amplifier, means directly connecting said frequency determining circuit to certain electrodes of the amplifier, a variable impedance load, means connecting said load to certain electrodes of said amplifier, and a variable condenser connecting the anode of said amplifier with a point in said frequency determining circuit of opposite high frequency potential from the point to which the grid of said amplifier is connected.

A wave transfer system including a space discharge oscillation generator, a tuned circuit comprising two impedances of' like sign and an impedance of opposite sign for determining the frequency of oscillations ti l Sill

produce l by said generator, a space discharge amplifier having input and out-put terminals, means directly connecting said input iern'iinals across one of said impedances oil like sign, a variable impedance load, means connecting said load across said output terminals, and a balancing, condenser connecting the output circuit of said aniplie tier to the other of said impedances of like sign.

6. in a circuit including a source of high frequency oscillations, an amplifier therefor and a load circuit, means comprising a tuned circuit for governing the frequency of the oscillations and for coupling the oscillation generator to the amplifier, and means comprising an impedance element directly connected in energy flow relation between the load circuit and the tuned circuit for preventing the impedance of the load circuit from eli'ecting the frequency of said oscillations.

7. In a space discharge system, a source of high frequency oscillations, a space discharge amplifier having, inherent capacity, means for coupling said source to said amplifier, a variable impedance load connected to said amplifier, 21 tuned circuit including said coupling means as a unit for establishing the frequency of said oscillations, and a balancing condenser directly connected between said load and said tuned circuit to prevent variations in load impedance from altering the frequency of said oscillations.

In Witness whereof, I hereunto subscribe my name this 20th day of April, A. 1)., 1925.

JOHN F. FARBINGTON. 

